/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
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 *
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 *
 */

package java.io;


/**
 * A character stream whose source is a string.
 *
 * @author Mark Reinhold
 * @since JDK1.1
 */

public class StringReader extends Reader {

  private String str;
  private int length;
  private int next = 0;
  private int mark = 0;

  /**
   * Creates a new string reader.
   *
   * @param s String providing the character stream.
   */
  public StringReader(String s) {
    this.str = s;
    this.length = s.length();
  }

  /**
   * Check to make sure that the stream has not been closed
   */
  private void ensureOpen() throws IOException {
    if (str == null) {
      throw new IOException("Stream closed");
    }
  }

  /**
   * Reads a single character.
   *
   * @return The character read, or -1 if the end of the stream has been reached
   * @throws IOException If an I/O error occurs
   */
  public int read() throws IOException {
    synchronized (lock) {
      ensureOpen();
      if (next >= length) {
        return -1;
      }
      return str.charAt(next++);
    }
  }

  /**
   * Reads characters into a portion of an array.
   *
   * @param cbuf Destination buffer
   * @param off Offset at which to start writing characters
   * @param len Maximum number of characters to read
   * @return The number of characters read, or -1 if the end of the stream has been reached
   * @throws IOException If an I/O error occurs
   */
  public int read(char cbuf[], int off, int len) throws IOException {
    synchronized (lock) {
      ensureOpen();
      if ((off < 0) || (off > cbuf.length) || (len < 0) ||
          ((off + len) > cbuf.length) || ((off + len) < 0)) {
        throw new IndexOutOfBoundsException();
      } else if (len == 0) {
        return 0;
      }
      if (next >= length) {
        return -1;
      }
      int n = Math.min(length - next, len);
      str.getChars(next, next + n, cbuf, off);
      next += n;
      return n;
    }
  }

  /**
   * Skips the specified number of characters in the stream. Returns
   * the number of characters that were skipped.
   *
   * <p>The <code>ns</code> parameter may be negative, even though the
   * <code>skip</code> method of the {@link Reader} superclass throws
   * an exception in this case. Negative values of <code>ns</code> cause the
   * stream to skip backwards. Negative return values indicate a skip
   * backwards. It is not possible to skip backwards past the beginning of
   * the string.
   *
   * <p>If the entire string has been read or skipped, then this method has
   * no effect and always returns 0.
   *
   * @throws IOException If an I/O error occurs
   */
  public long skip(long ns) throws IOException {
    synchronized (lock) {
      ensureOpen();
      if (next >= length) {
        return 0;
      }
      // Bound skip by beginning and end of the source
      long n = Math.min(length - next, ns);
      n = Math.max(-next, n);
      next += n;
      return n;
    }
  }

  /**
   * Tells whether this stream is ready to be read.
   *
   * @return True if the next read() is guaranteed not to block for input
   * @throws IOException If the stream is closed
   */
  public boolean ready() throws IOException {
    synchronized (lock) {
      ensureOpen();
      return true;
    }
  }

  /**
   * Tells whether this stream supports the mark() operation, which it does.
   */
  public boolean markSupported() {
    return true;
  }

  /**
   * Marks the present position in the stream.  Subsequent calls to reset()
   * will reposition the stream to this point.
   *
   * @param readAheadLimit Limit on the number of characters that may be read while still preserving
   * the mark.  Because the stream's input comes from a string, there is no actual limit, so this
   * argument must not be negative, but is otherwise ignored.
   * @throws IllegalArgumentException If {@code readAheadLimit < 0}
   * @throws IOException If an I/O error occurs
   */
  public void mark(int readAheadLimit) throws IOException {
    if (readAheadLimit < 0) {
      throw new IllegalArgumentException("Read-ahead limit < 0");
    }
    synchronized (lock) {
      ensureOpen();
      mark = next;
    }
  }

  /**
   * Resets the stream to the most recent mark, or to the beginning of the
   * string if it has never been marked.
   *
   * @throws IOException If an I/O error occurs
   */
  public void reset() throws IOException {
    synchronized (lock) {
      ensureOpen();
      next = mark;
    }
  }

  /**
   * Closes the stream and releases any system resources associated with
   * it. Once the stream has been closed, further read(),
   * ready(), mark(), or reset() invocations will throw an IOException.
   * Closing a previously closed stream has no effect.
   */
  public void close() {
    str = null;
  }
}
